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Migh I quote from here:
Mac OS X is the only major consumer operating system that comes complete with a fully configured and ready-to-use Java runtime and development environment. Professional Java developers are increasingly turning to the feature-rich Mac OS X as the operating system of choice for both Mac-based and cross-platform Java development projects. Mac OS X includes the full version of J2SE 1.5, pre-installed with the Java Development Kit (JDK) and the HotSpot virtual machine (VM), so you don't have to download, install, or configure anything.
 
Since you don't have your OSX CDs anymore, sign up for Apple Developer Connection and Download it from here, where it says "Xcode
Xcode is a free download for Mac OS X development..."
 
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